Modern technologies are developing prosperously. Novel information products are introduced frequently for satisfying people's various needs. Most of the early displays are cathode ray tube (CRT) displays. Owing to their huge size, tremendous power consumption, and radiation threats to the health of long-term users, current commercial displays are gradually replaced by liquid crystal displays (LCDs). LCDs have the advantages of small size, low radiation, and low power consumption, making them become the mainstream in the market.
LCDs display images by controlling the transmissivity of liquid crystal cells according to data signals. Active-matrix LCDs adopt active control of switching devices. Thereby, they are beneficial in displaying motion pictures. Thin film transistors (TFTs) are mainly applied to related device of active-matrix LCDs.
Please refer to FIG. 1, which shows a schematic diagram of the displaying device according to the prior art. As shown in the figure, the displaying device comprises a display panel 10, a data driving circuit 14, and a charge pump 16. The data driving circuit 14 comprises a plurality of digital-to-analog converting circuits (DAC) 141 and a plurality of operational amplifiers 143. The plurality of digital-to-analog converting circuits 141 produce a selecting voltage Vsel to the plurality of operational amplifiers 143, respectively. The plurality of operational amplifiers 143 generate a plurality of driving signals SL to a plurality of equivalent capacitors C of the display panel 10 according to the selecting voltage Vsel, respectively, for driving the display panel to display images. The charge pump 16 is connected to the differential circuits 1431 of the plurality of operational amplifiers 143 and the driving circuits simultaneously, and supplies a fixed supply voltage VP to the differential circuits 1431 and the driving circuits 1433 according to a reference voltage VDD to make them operate.
According to the above description, the charge pump 16 of the displaying device according to the prior art provides the fixed supply voltage VP to the differential circuits 1431 and the driving circuits 1433, so that the operational amplifiers 143 can generate the plurality of driving signals SL. Nonetheless, the shortcoming of this method is that no matter the voltage required by the plurality of equivalent capacitors C of the display panel is greater or smaller than the reference voltage VDD, the charge pump 16 provides invariably the supply voltage VP to the plurality of operational amplifiers 143. Thereby, when no excessively high supply voltage VP is required, that excessively high supply voltage VP results in excess power consumption.
Accordingly, for solving the problem described above, the present invention provides a voltage boosting circuit capable of modulating duty cycle automatically, which supplies the power required by a loading by charging and discharging an inductor and modulating the duty cycle automatically according to the power required by the loading. Thereby, the purposes of reducing excess power consumption and saving power can be achieved.